The word ‘fact’ is always likely to make biologists tremble in their boots, as there are so many exceptions to every rule; but one such ‘fact’ is virtually certain about oxygenic photosynthesis – it only evolved once.
— Nick Lane, in his discussion of the evolution of photosynthesis, page 73, in Life Ascending: The Ten Great Inventions of Evolution, a book now studied in CC106: Biodiversity
